ctdbd: Remove command-line option --debug-hung-script

ctdbd: Remove command-line option --debug-hung-script

Use an environment variable instead.  This just means that the
initscript exports CTDB_DEBUG_HUNG_SCRIPT and the code checks for the
environment variable.

The justification for this simplification is that more debug options
will be arriving soon and we want to handle them consistently without
needing to add a command-line option for each.  So, the convention
will be to use an environment variable for each debug option.

Signed-off-by: Martin Schwenke <martin@meltin.net>